package Test;

import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.stream.Collectors;

public class TestDemo17 {
    public static void main(String[] args) {
        HashMap<String,String> hashMap = new HashMap<>();
        hashMap.put(null,"1");
        System.out.println(hashMap.get(null));
        Map<String, String> stringStringMap = Collections.synchronizedMap(hashMap);
        stringStringMap.put(null,"2");
    }
}
